This study explores how the distinctive Korean age reckoning, the Confucian age culture, and the school-entry-cutoff date affect the decisions of parents on both birth and school-entry timing for their children in Korea. There is a traditional method of age calculation in Korea that all people get one year older on January 1. Korea also has a distinctive age culture influenced by Confucianism. I find a substantial amount of birth and school-entry timing selections around the Korean age-cutoff date, January 1. The estimation results show that children born in January and February delayed school entry by 18.2–21.2 percentage points more than those born in November and December and 24% of births moved from one week before January 1 to one week after when the school-entry cutoff was March 1. After the school-entry cutoff has changed to January 1, children barely delay school enrollment, while more births are moved from December to January: 42% of births are shifted within the 7-day window. These behaviors are made by two motives: (1) parents want their children to have the same Korean age with their classmates because of the Confucian age culture; (2) they also want their children to be relatively older to have academic advantages.